A positive temperature coefficient (PTC) element exhibits a PTC effect that renders the same usefulness as a circuit protecting device, such as a resettable fuse. The PTC element includes a PTC polymer material and first and second electrodes attached to two opposite surfaces of the PTC polymer material.
The PTC polymer material includes a polymer matrix that contains a crystalline region and a non-crystalline region, and a particulate conductive filler dispersed in the non-crystalline region of the polymer matrix and formed into a continuous conductive path for electrical conduction between the first and second electrodes. The PTC effect is a phenomena that, when the temperature of the polymer matrix is raised to its melting point, crystals in the crystalline region start melting, which results in the generation of a new non-crystalline region. As the new non-crystalline region is increased to an extent and merges into the original non-crystalline region, the conductive path of the particulate conductive filler will become discontinuous and the resistance of the PTC polymer material will be sharply increased, thereby resulting in an electrical disconnection between the first and second electrodes.
Tungsten carbide particles are used in PTC elements as the particulate conductive filler. The existing PTC elements containing the tungsten carbide particles are usually operated at 6 Vdc. However, when such PTC elements are operated at a relatively high voltage (e.g., 12 Vdc), the stability thereof is unsatisfactory and needs to be improved.